Volume 10 (1991)

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Colour Illustrations
(Eurographics Association, 1991) -
Computational Physics : A Modeler - Simulator for animated physical Objects
(Eurographics Association, 1991) Luciani, Annie; Jimenez, Stephane; Florens, Jean Loup; Cadoz, Claude; Raoult, Olivier
Physical modeling for animation is now firmly established. The present aim is to design and build a structured and well-defined tool rather than merely specific algorithms to simulate physical knowledge. We will first define the basic functions of a modeler - simulator for physical modeling which enables operator gestural control, and where the simulation processes are real time oriented. These constraints cannot be achieved by any kind of models and algorithms. Concerning the theoretical elements, the choice of the underlying Physics and the categorization of interactions will be presented. We will then introduce the Cordis-Anima system, its constructive langage, its real time simulator and its force feedback gestural transducers. Finally, we will describe, with some examples, how we model, simulate and manipulate a large variety of physical objects and scenes with our system.
The GKS Input Model in Manifold
(Blackwell Science Ltd and the Eurographics Association, 1991) Soede, Dirk; Arbab, Farhad; Herman, Ivan; Ten Hagen, Paul J. W.
This paper describes the specification of the GKS input model in Manifold. The aim of the work reported in this paper was two-fold: first, to review the communication patterns implied by the GKS input model, and second, to evaluate the suitability of the Manifold language as a tool for defining complex dynamic interaction patterns that are common in non-trivial user interfaces.The GKS input model is also adopted by all more recent ISO graphics standard documents. A more formal scrutiny of the inter-communication of the components of this model, excluding the implementation details of their functionality, is instructive in itself. It can reveal directions for improvement of its shortcomings and for generalization of its strengths for the ongoing effort to define the functionality of future graphics packages.Manifold is a language for describing inter-process communications. Processes in Manifold communicate by means of buffered communication links called streams and by reacting to events raised asynchronously by other processes. Our experience shows that Manifold is a promising tool for describing systems of cooperating parallel processes. Our Manifold specification of the GKS input model offers a very flexible way to structure user defined logical input devices. Furthermore, it is simple and modular enough to allow easy extensions to include more functionality by local modifications. As such, it can serve as a basis for possible extensions and enhancements envisioned for future graphics packages.1987 CR Categories: C.1.2, C.1.3, C.2.m, D.1.3, F.1.2, I.1.3, I.3.6, I.3.4.1885 Mathematical Subject Classification: 68N99, 68Q10,68U05.
Triangle Sets in PHIGS PLUS: a Valuable Link with Finite Element Modeling
(Blackwell Science Ltd and the Eurographics Association, 1991) Bakker, Miente
At the ISO/IEC editing meeting on PHIGS PLUS1 in Villars sur Ollon, Switzerland from 9 to 14 September 1990, an additional output primitive was added to PHIGS PLUS: TRIANGLE SET 3 WITH DATA together with its 2D shorthand. The principal reason for that addition was that only triangular primitives admit uniquely defined interpolation of data (colours, normals, etc.) across the facet.However, an additional advantage of this new primitive is its value for the visualization of scientific computing results. It corresponds in a very pleasant way with the Finite Element Method using piecewise linear blending functions on a triangular partition of the function domain.In this paper, an outline will be given of the possible use of this function by Finite Element engineers.1983 CR Categories: G.1.1, G.1.2,I.3.2,I.3.5,I.3.7, J.6.
Cartographic Algorithms: Problems of Implementation and Evaluation and the Impact of Digitising Errors
(Blackwell Science Ltd and the Eurographics Association, 1991) Visvalingam, M.; Whyatt, J.D.
Cartographic generalisation remains one of the outstanding challenges in digital cartography and Geographical Information Systems (GIS). It is generally assumed that computerisation will lead to the removal of spurious variability introduced by the subjective decisions of individual cartographers. This paper demonstrates through an in-depth study of a line simplification algorithm that computerisation introduces its own sources of variability. The algorithm, referred to as the Douglas-Peucker algorithm in cartographic literature, has been widely used in image processing, pattern recognition and GIS for some 20 years. An analysis of this algorithm and study of some implementations in wide use identify the presence of variability resulting from the subjective decisions of software implementors. Spurious variability in software complicates the processes of evaluation and comparison of alternative algorithms for cartographic tasks. No doubt, variability in implementation could be removed by rigorous study and specification of algorithms. Such future work must address the presence of digitising error in cartographic data. Our analysis suggests that it would be difficult to adapt the Douglas-Peucker algorithm to cope with digitising error without altering the method.
Million-Point Sculptures
(Blackwell Science Ltd and the Eurographics Association, 1991) Pickover, Cliff
Visually interesting chaotic attractors resembling sculpture are described.
A Picture Archive Browser
(Blackwell Science Ltd and the Eurographics Association, 1991) Willis, Philip; Hunter, Andrew
We describe an implementation of a networked picture browser. The system offers a pictorial interface to pictorial data, relieves the users of thinking about the underlying filing system, provides managerial tools for installing, moving and deleting pictures, offers graded access and picture sharing and supports a number of picture formats, including hierarchical encodings.
Radiosity for Furry Surfaces
(Eurographics Association, 1991) Chen, Hong; Wu, En-Hua
Though radiosity method is an advanced rendering technique of global illumination, it is still not sufficiently to cope with many natural phenonmena such as furry surfaces. The rendering of furry surfaces has been a long outstanding problem in image synthesis. Therefore, it is of significance to develop an approach to incorporate the rendering of furry surfaces into radiosity method. By combining the concept of texel with the furry radiosity map , established from the radiosity calculation based on the proposed furry form-factor in the paper, a new radiosity algorithm has been developed to produce the images of furry surfaces.
Construction Techniques of Graphic, Direct-Manipulation User Interfaces
(Eurographics Association, 1991) Preea, Wolfgang; Pornberger, Gustav; Sikora, Hermann
This paper deals with human-computer interaction in several ways. On the one hand it presents the roots of interactive, graphic user interfaces and how such interfaces are implemented on the abstraction level of programming languages: The construction of graphic, direct-manipulation interfaces with conventional programming techniques is compared with an object-oriented approach based on powerful class libraries (called user interface application frameworks). Although application frameworks substantially ease the building of highly interactive applications the abstraction level is considered to be too low to support prototyping such interfaces in a comfortable way. Hence we portray DICE1 (Dynamic Interface Creation Environment), a tool for prototyping graphic user interfaces implemented itself in an object-oriented manner. In particular this paper discusses the question of how dynamic behavior can be added to a user interface prototype. It also presents a useful and powerful way to combine conventionally developed and object-oriented software systems.
Object-Oriented Data Modelling for Graphics Databases: a Declarative Approach
(Blackwell Science Ltd and the Eurographics Association, 1991) Bhalla, Neelam; Balasundaram, S.
This paper presents a new scheme to integrate the declarative approach to graphics and object-oriented data modelling techniques to form a fruitful symbiosis for constraint-based graphics database systems. It has rich modelling constructs to describe graphics data and allows sharing of representation. It also provides useful mechanisms for management of integrity constraints. We have also identified important classes of constraints in the context of object-oriented graphics database systems. Examples are given for maintenance of constraints at the time of insertion, deletion and modification.
Time Complexity of Monte Carlo Radiosity
(Eurographics Association, 1991) Shirley, Peter
The time complexity of Monte Carlo radiosity is discussed, and a proof is given that the expected number of rays required to produce a satisfactory radiosity solution for N zones is O(N). A satisfactory solution is defined to be one in which the variance of radiance estimates for each zone is below a predefined threshold. The proof assumes that the radiance is bounded, and the area ratio of the largest to smallest zone is bounded.
Fat curves
(Blackwell Science Ltd and the Eurographics Association, 1991) Yao, C.; Rokne, J.
Fat curves in two-dimensional Euclidean space are discussed. Previous work on fat curves is reviewed and a new definition is given for a fat curve having a smooth axis. The joining of two fat curves is discussed and a technique for scan-converting fat curves is presented.
Liberation from Flatland: 3D Interaction Based on the Desktop Bat
(Eurographics Association, 1991) Slater, Mel; Davison, Allan
A novel device for 3D interaction is introduced, the Desktop Bat. This device is an evolutionary development of a mouse. It is like a mouse in that it is used on a desktop, but provides 5 degrees of freedom since in conjunction with translations it can be used to effect rotations about any combination of the principal axes. We discuss the requirements for 3D interaction which led to the design of the Desktop Bat, and the interaction models and software which allow it to be used as a 6 degrees of freedom input device.
Geometric Modelling from Range Image Data
(Eurographics Association, 1991) Schmitt, Francis; Cken, Xin; Du, Wen-Hui
An adaptive surface fitting algorithm is proposed for modelling the digitized surface of a real object described by an array of 3D points sampled on a rectangular mesh and stored in the form of a range image. A G1 -piecewise approximation of the data is obtained by using an adaptive top-down method which combines the Delaunay triangulation technique with a triangular Gregory-Bezier patch model (tGB). The method begins with a rough approximation of the surface and progressively refines it in successive steps in the regions where the accuracy requirement of the approximation is not satisfied. The method, therefore, is essentially a local process. An optimization approach is used to obtain a G '-continuous piecewise approximation where each tGB patch is as smooth and regular as possible. Some experimental results are given to demonstrate the potential usefulness of this approach for the geometric modelling from range image data.
Low Sampling Densities using a psychovisual approach
(Eurographics Association, 1991) Bouville, Christian; Tellier, Pierre; Bouatouch, Kadi
It has long been observed that the keenness of sight is lower for diagonal directions than for horizontal or vertical ones. This anisotropy of the human eye response can be exploited by using a non-orthogonal sampling pattern with a reduced sampling density. After an introduction to the two-dimensional sampling theory, it is shown that quincunx sampling is well suited to this characteristic. Then a sampling scheme based on this approach is described. This effectively leads to halving the sampling density and thereby the computing time of ray-traced pictures.
Animation of Landscapes Using Satellite Imagery
(Eurographics Association, 1991) Geymayer, Barbara; Prantl, Manfred; Müller-Seelich, Heimo; Tabatabai, Behnam
The paper presents methods to animate synthetic landscapes. The modeling of the landscape, the interactive specification of the flight path and the simulation of an explosion are described. The landscape is visualized by superimposing texture information computed from different satellite data onto a digital elevation model. A pyramid data structure is used to store the texture and digital elevation model data in different resolutions. This approach allows the generation of pictures with constant data density in an efficient way. The flight path is modeled interactively using a wireframe representation of the landscape. An explosion is simulated using physically modeled trajectories of the exploding parts. The approach is explained in the context of the “ERZBERG” animation in which an impressive flight through a valley towards the exploding Erzberg mountain has been generated.
Interrogation of Offsets of Polynomial Surface Patches
(Eurographics Association, 1991) Vafiadou, Maria - Eleni; Patrikalakis, Nicholas M.
This paper presents an algorithm for computing the intersection of the offset (or parallel) surface of a polynomial surface patch ( rogenitor) of arbitrary degree, with a straight line. The rogenitor patch is expressed in the tensor product Bernstein form. The intersection problem is reformulated in terms of computing the intersection of two algebraic curves within the parameter s ace of the patch. The tensor product Bernstein form is emplo ed for the representation of these algebraic curves. The solution method is based on subdivision relying on the convex hull roperty of the Bernstein representation of algebraic curves and minimization techniques. The resulting algorithm can form the basis for accurate visualization of offset surfaces through ray tracing methods.
Using temporal and spatial coherence for accelerating the calculation of animation sequences
(Eurographics Association, 1991) Gröller, Eduard; Purgathofer, Werner
Ray tracing is a well known technique for generating realistic images. One of the major drawbacks of this approach are the extensive computational requirements for image calculation. When generating animation sequences frame by frame the computational cost might easily become intolerable. In the last years several methods have been devised for accelerating the computational speed by using spatial and temporal coherence. While these techniques work only under certain restrictions, a new approach is presented in this paper which leads to a considerable speed-up of the calculation process without putting any limitations on camera or object movement. In principle, the method is an extension of /ArKi87/, where rays are considered points in 5D space, by the time dimension. CSG is used for object description and has been modified correspondingly to allow easy use of coherence properties. The paper describes the theoretical background and the main concepts of a practical implementation.
The Formal Specification of Level la of GKS
(Blackwell Science Ltd and the Eurographics Association, 1991) Damnjanovic, Ljiljana B.
In this paper the formal specification of a part of level la of GKS is given in the algebraic specification language OBJ. It shows that it is possible to produce a formal specification of a substantial part of GKS which is of manageable size and complexity specifying the appropriate level of abstraction of the system and using a suitable formal technique.
Sampling and Anti-Aliasing of Discrete 3-D Volume Density Textures
(Eurographics Association, 1991) Sakas, Georgios; Gerth, Matthias
In recent years, a number of techniques have been developed for rendering volume effects (haze, fog, smoke, clouds, etc.) in order to enhance reality in computer-generated imagery as well as to improve the performance of flying, ship, and driving optical simulators. For modeling such effects, volume 'density' objects are used, which are defined by their density distribution in 3-D space. For such a description a three-dimensional voxel field (solid texture) is usually used. Since we deal with 3-D textures, the methods used for sampling 2-D pixel fields cannot always be employed. In this paper, we propose two variants of a new technique for sampling and anti-aliasing 3-D density voxel fields. First, we point out the problems which occur when such 3-D textures are sampled, especially when the point sampling Monte-Carlo method is used. 'Distance sampling' and 'pyramidal-volume sampling' are then introduced. The first ,technique samples the texture along a straight line defined by the eye position and the pixel midpoint, whereas the pyramidalvolume technique approximately samples the volume of the pyramid defined by the eye and the four pixel comers. In comparison to other existing methods, both methods greatly reduce aliasing and calculation time. Especially the second one provides a constant-time filtering, whereby minimizing the number of texture evaluations. In the last paper section we demonstrate the applicability of the proposed methods for animation as well as for visualization purposes.

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